Self-organized metal alloys for wear applications

ABSTRACT

A two-phase metallic alloy comprising precipitates of Ag possessing a volume-averaged diameter of less than about 500 nm dispersed in a matrix selected from the group consisting of Ni, Fe, combinations of Ni with Cu and combinations of Fe with Cu.

FIELD OF THE INVENTION

The invention relates to self-organized metal alloys for wear applications. More particularly, the invention relates to two-phase metallic alloys having nanometer-size precipitates of Ag dispersed in a matrix of Ni, Fe, Ni and Cu or Fe and Cu.

BACKGROUND OF THE INVENTION

High resistance to frictional wear requires that materials in contact: (i) are hard, in order to minimize the damage introduced by high contact stresses; and (ii) possess high toughness, so that despite the accumulation of plastic deformation near the sliding surfaces, the volume of debris generated is small. These two main requirements, however, are often conflicting, since many very hard or super hard materials such as oxides, nitrides and carbides are also brittle, and thus have poor toughness. Conversely, tough materials generally do not possess sufficient hardness. The common approach for solving this dilemma is to use composite materials, which combine high hardness and high toughness. Examples of such composites are WC/Co tool bits.

One important limitation to these traditional approaches, however, is that the wear process itself modifies the microstructure of the coatings, often resulting in a gradual degradation in their performance. In the past two decades, investigations have been made into whether the wear-induced evolution of the composite microstructure could actually result in an improvement of the wear resistance. Such materials are sometimes referred to as self-adapting or self-organizing. Successful examples include materials where sliding friction results in the spontaneous formation of lubricious films (often called tribolayers or tribofilms or third bodies). Most of the prior work, however, did not include the re-organization of the material bulk microstructure near the contacting surfaces. While Cu—Ag alloys have been evaluated for high wear resistance applications, Acta Materialia, 72 (2014) 148-158, further improvements are nevertheless needed.

It has unexpectedly been discovered that a particularly designed metal alloy system can improve wear resistance, and thus increase the lifetime of mechanical systems that contain parts subjected to friction wear, such as bearings. These metal alloy systems also reduce the probability of a catastrophic failure during loss of external lubricants, since the wear-induced nanolayered structure can act as a solid lubricant. By relying on a self-adapting reaction triggered by the wear process itself, the metal alloy provides wear resistance only where and when it is needed. Thus, there is no need to process the entire surface of the sample before its use, as typically practiced when applying wear-resistant coatings.

SUMMARY OF THE INVENTION

In one embodiment, the subject matter of the present disclosure relates to a two-phase metallic alloy comprising precipitates of Ag possessing a volume-averaged diameter of less than about 500 nm dispersed in a matrix selected from the group consisting of Ni, Fe, combinations of Ni with Cu and combinations of Fe with Cu.

In another embodiment, the subject matter of the present disclosure relates to a method of making a two-phase metallic alloy, comprising providing a powder mixture selected from the group consisting of powder mixtures of Ag and Ni; Ag and Fe; Ag, Ni and Cu; and Ag, Fe and Cu, subjecting the powder mixture to high-energy ball milling to provide a nanocomposite, compressing the nanocomposite to provide a solid form, and optionally annealing the solid form to provide a two-phase metallic alloy comprising precipitates of Ag possessing an average size of less than about 500 nm.

In still another embodiment, the subject matter of the present disclosure relates to an article comprising an alloy of powder mixtures selected from the group consisting of powder mixtures of Ag and Ni; Ag and Fe; Ag, Ni and Cu; and Ag, Fe and Cu.

In another embodiment, the subject matter of the present disclosure relates to a substrate coated with an alloy of powder mixtures selected from the group consisting of powder mixtures of Ag and Ni; Ag and Fe; Ag, Ni and Cu; and Ag, Fe and Cu.

In still another embodiment, the subject matter of the present disclosure relates to a method comprising coating a substrate with the alloy of powder mixtures selected from the group consisting of powder mixtures of Ag and Ni; Ag and Fe; Ag, Ni and Cu; and Ag, Fe and Cu.

In another embodiment, the invention relates to a two-phase metallic alloy comprising precipitates of Ag possessing a volume-averaged diameter of less than about 500 nm dispersed in a matrix selected from at least one of W, Mo, Cr, Ni, C, Al, Ti, Cu, Fe, Mn, S, Si, N, Co, and Nb, wherein at least one of Ni or Fe is present in an amount of at least 35 atomic percent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates XRD patterns of as-pressed, pure Ni and Ni₄₅Cu₄₅Ag₁₀ ternary alloy.

FIG. 2(a) illustrates HAADF-STEM images of as annealed Ni₉₀Ag₁₀ binary alloy.

FIG. 2(b) illustrates an ND-SD cross-sectional HAADF-STEM image after wear against SS440C at a 0-2 μm depth below the sliding surface.

FIG. 2(c) illustrates an ND-SD cross-sectional HAADF-STEM image after wear against SS440C at a 2-4 μm depth below the sliding surface.

FIG. 2(d) illustrates an ND-SD cross-sectional HAADF-STEM image after wear against SS440C at a 4-6.0 μm depth below the sliding surface.

FIG. 3(a) illustrates wear track surface morphology of Ni₉₀Ag₁₀ annealed at 600° C. and against SS440 stainless steel.

FIG. 3(b) illustrates wear debris of Ni₉₀Ag₁₀ annealed at 600° C. and against SS440 stainless steel.

FIG. 3(c) illustrates energy dispersive X-ray spectra of Ni₉₀Ag₁₀ annealed at 600° C. and against SS440 stainless steel.

FIG. 3(d) illustrates wear track surface morphology of Ni₈₀Cu₁₀Ag₁₀ annealed at 600° C. and against SS440 stainless steel.

FIG. 3(e) illustrates wear debris of Ni₈₀Cu₁₀Ag₁₀ annealed at 600° C. and against SS440 stainless steel.

FIG. 3(f) illustrates energy dispersive X-ray spectra of Ni₉₀Ag₁₀ annealed at 600° C. and against SS440 stainless steel.

FIG. 4 illustrates chemical nanolayering in a two-phase Ni₉₀Ag₁₀ alloy subjected to dry sliding wear, with a load of 10 N at room temperature at a sliding speed of 0.25 m/s. HAADF-STEM image: Ag appears as bright, Ni dark.

FIG. 5 illustrates steady state wear rate in Ni₉₀Ag₁₀ nanocomposites with various initial precipitate sizes, obtained by annealing at temperatures ranging from 300° C. to 900° C. The corresponding Ag initial precipitate sizes are 15 nm, 90 nm, and 1 μm, respectively.

DETAILED DESCRIPTION OF THE INVENTION

The subject matter of the present disclosure provides metallic materials for applications requiring high resistance to frictional wear, including mechanical systems such as bearings and dynamic seals. These metallic materials rely on a self-adapting reaction in two-phase composite materials subjected to wear. This reaction, near the wear surface, transforms the initial isotropic microstructure of the composite into self-organized nanolaminates. This nanolaminate structure provides an increase in wear resistance.

In one embodiment, the subject matter of the present disclosure relates to a two-phase metallic alloy comprising precipitates of Ag possessing a volume-averaged diameter of less than about 500 nm dispersed in a matrix selected from the group consisting of Ni, Fe, combinations of Ni with Cu and combinations of Fe with Cu. In another embodiment, the subject matter of the present disclosure relates to a two-phase metallic alloy comprising precipitates of Ag possessing a volume-averaged diameter of less than about 500 nm dispersed in a matrix selected from at least one of W, Mo, Cr, Ni, C, Al, Ti, Cu, Fe, Mn, S, Si, N, Co, and Nb, wherein at least one of Ni or Fe is present in an amount of at least 35 atomic percent on the basis of the metallic alloy.

Self-Organized Metals

Self-organized metals are often encountered when service conditions drive materials into non-equilibrium states. This is frequently observed in metallic alloys subjected to severe plastic deformation, for instance during alloy fabrication (mechanical alloying), during shaping (rolling), during joining (friction stir welding), or in service, e.g., in components subjected to sliding wear or erosion wear. Self-organization often results in the spontaneous stabilization of nanostructures, leading to local modifications of mechanical properties. The metal alloys of the present disclosure adapt when subjected to wear by spontaneously forming nanostructures that reduce friction and wear. The plastic deformation induced by wear below sliding surfaces can lead to the self-organization of metallic alloys microstructure, i.e., chemical nanolayering.

Precipitates of Ag

The two-phase metallic alloy of the present disclosure contains precipitates of Ag that are immiscible in the matrix. Preferably, the Ag precipitates possess a volume-averaged diameter of less than about 500 nm. More preferably, the Ag precipitates possess a volume-averaged diameter of between 100 and 400 nm, and even more preferably, a volume-averaged diameter of between 100 and 300 nm.

It has unexpectedly been found that the precipitate size affects wear resistance. The precipitate size can be varied by annealing the alloy at various temperatures, up to 900° C. Preferably, the annealing temperature is from 20° C. to 800° C., more preferably, from 250° C. to 700° C., even more preferably from 275° C. to 625° C. The alloys, fabricated by ball-milling and warm compaction, contain two phases: a nearly pure matrix, e.g., Ni, and nearly pure Ag precipitates, owing to the large immiscibility between Ni and Ag. During sliding wear, the Ag precipitate size can be correctly selected by the appropriate annealing conditions, where chemical nanolayering is observed just below the wear surface, resulting in a low wear rate. Preferably, the nanolayering is located 200 nm to 5 μm below the wear surface. In contrast, if the initial Ag precipitates are too small or too large, the nanolayers do not form or incompletely form, so that the wear rate can be up to 10 times larger, or even higher.

Matrix

The metal alloys of the present disclosure also contain a matrix, within which the Ag precipitate is dispersed.

In one embodiment, the matrix can be Ni, Fe, combinations of Ni and Cu, or combinations of Fe and Cu. When the alloy contains Ni, Ag is preferably present in an amount ranging from about 5 to about 20 atomic percent, and Ni is present in the alloy in an amount ranging from about 50 to about 95 atomic percent. When the alloy contains Ni and Cu, Ag is preferably present in an amount ranging from about 5 to about 20 atomic percent, Ni is preferably present in an amount ranging from about 50 to about 90 atomic percent and Cu is preferably present in an amount ranging from about 5 to about 45 atomic percent.

When the alloy contains Fe, Ag is preferably present in an amount ranging from about 5 to about 20 atomic percent, and Fe is present in the alloy in an amount ranging from about 50 to about 95 atomic percent. When the alloy contains Fe and Cu, Ag is preferably present in an amount ranging from about 5 to about 20 atomic percent, Fe is preferably present in an amount ranging from about 50 to about 90 atomic percent and Cu is preferably present in an amount ranging from about 5 to about 45 atomic percent. I

n another embodiment, the matrix is selected from at least one of W, Mo, Cr, Ni, C, Al, Ti, Cu, Fe, Mn, S, Si, N, Co, and Nb, wherein at least one of Ni or Fe is present in an amount of at least 35 atomic percent on the basis of the metal alloy.

Preferably, the matrix is selected from at least one of W, Mo, Cr, Ni, C, Al, Ti, Cu, Fe, Mn, S, Si, N, Co, and Nb. More preferably, the matrix is selected from at least one of W, Mo, Cr, Ni, C, Al, Ti, Fe, Mn, S, Si, N, Co, and Nb. Even more preferably, the matrix is selected from at least one of Ni, Fe, Cr, Mo, Ti, and W. Most preferably, the matrix is selected from at least one of Ni and Fe.

Examples of the matrix include Incoloy® Alloy 330, Incoloy® Alloy 800, Incoloy® Alloy 800H, Incoloy® Alloy 800HT, Incoloy® Alloy 803, Incoloy® Alloy 840, Incoloy® Alloy 890, Inconel® Alloy 600, Inconel® Alloy 601, Inconel® Alloy 617, Nickel 200, Nickel 201, Duranickel® Alloy 301, Monel® Alloy 400, Monel® Alloy R-405, Monel® Alloy K-500, Inconel® Alloy 800, Inconel® Alloy 22, Inconel® Alloy 625, Inconel® Alloy 625SLCF®, Inconel® Alloy 686, Inconel® Alloy 690, Inconel® Alloy C-276, Inconel® Alloy G-3, Incoloy® Alloy 800, Incoloy® Alloy 825, Incoloy® Alloy 864, Incoloy® Alloy 20, or Incoloy® Alloy 25-6HN.

Preferably, examples of the matrix include Incoloy® Alloy 330, Incoloy® Alloy 800, Incoloy® Alloy 800H, Incoloy® Alloy 800HT, Incoloy® Alloy 803, Incoloy® Alloy 840, Incoloy® Alloy 890, Inconel® Alloy 600, Inconel® Alloy 601, Inconel® Alloy 617, Nickel 200, Nickel 201, Duranickel® Alloy 301, Inconel® Alloy 800, Inconel® Alloy 22, Inconel® Alloy 625, Inconel® Alloy 625SLCF®, Inconel® Alloy 686, Inconel® Alloy 690, Inconel® Alloy C-276, Incoloy® Alloy 800, Incoloy® Alloy 864.

The metal alloys of the present disclosure have improved hardness. Such alloys preferably have a hardness of 3 to 10 GPa when pressed at conditions of 1 GPa for 1 hour at 300° C.; a hardness of 2 to 10 GPa after pressing at 1 GPa for 1 hour at 300° C. and annealing at 600° C. for 1 hr; and 1 to 5 GPa after pressing for 1 hour at 300° C. and annealing at 900° C. for 1 hr.

In another embodiment, the subject matter of the present disclosure relates to a method of making a two-phase metallic alloy, comprising providing a powder mixture selected from the group consisting of powder mixtures of Ag and Ni; Ag and Fe; Ag, Ni and Cu; and Ag, Fe and Cu, subjecting the powder mixture to high-energy ball milling to provide a nanocomposite, compressing the nanocomposite to provide a solid form, and optionally annealing the solid form to provide a two-phase metallic alloy comprising precipitates of Ag having an average size of less than about 500 nm. For the purposes of this specification, the expression “high energy ball-milling” means combining a powder mixture with hard steel (or tungsten carbide) balls in a sealed vial, which is then subjected to energetic motion so as to induce repeated collisions between the powder particles and the balls. Such ball-milling can be performed in equipment such as an SPEX 8000 shaker mill or a Fritsch planetary mill pulverisette. Ball-milling is conducted to obtain a nanocomposite of the Ag precipitate and the matrix. For the purposes of this specification, the term nanocomposite means a microstructure consisting of precipitates of nanometric dimensions, typically from 1 to 100 nm, embedded in a matrix phase. One skilled in the art would recognize that nanocomposites differ from the solid solutions that may result from high-energy ball milling, e.g., in Cu—Ag systems, because the term solid solution means that the alloying element, in this case Ag, is fully dissolved in the matrix, whereas in the case of a Ni—Ag nanocomposite, the Ag atoms have gathered to form precipitates. Preferably, the ball milling is conducted at a temperature of 20° C. to 100° C., and for a time period of 5 to 24 hours.

The nanocomposite is then compressed to produce a solid form, preferably at a temperature of 200° C. to 300° C., with a compression force of 0.1 GPa to 1.2 GPa, at a pressure of 10⁻⁸ ton to 3×10⁻⁸ torr. The solid form preferably has a minimum density of 92% the theoretical density of that material, since the compaction can result in some residual porosity.

The solid form is then optionally annealed, preferably at a temperature of 20° C. to 800° C., more preferably, from 250° C. to 700° C., even more preferably from 275° C. to 625° C., and a pressure of 10⁻⁵ torr to 10⁻⁵ torr. Annealing the solid form is preferably performed if the Ag precipitate size in the as-milled state is not large enough to result in nanolayering and wear reduction.

When processed at the specified conditions, the two-phase metallic alloy comprises a wear surface and chemical nanolayering below the wear surface. Preferably, the chemical nanolayering extends from 1 μm to 5 μm below the wear surface.

Preferably, the powder mixture contains Ag and Ni, Ag and Fe, Ag, Ni and Cu or Ag, Fe and Cu. Preferably, when the powder mixture is Ag and Ni, the powder mixture has an atomic formula of Ni₉₀Ag₁₀ or Ni₈₀Ag₂₀. When the powder mixture is Ag, Fe and Cu, the powder mixture has an atomic formula of Ni₈₀Cu₁₀Ag₁₀ or Ni₄₅Cu₄₅Ag₁₀.

In still another embodiment, the subject matter of the present disclosure relates to an article comprising alloys of powder mixtures containing Ag and Ni, Ag and Fe, Ag, Ni and Cu or Ag, Fe and Cu. Preferably, such articles include seals, gears, and electric brushes.

In another embodiment, the subject matter of the present disclosure relates to a substrate coated with alloys of a powder mixture containing Ag and Ni, Ag and Fe, Ag, Ni and Cu or Ag, Fe and Cu described above. Preferably, the substrates are steels, stainless steels, Ni-base and Cu-base alloys.

In still another embodiment, the subject matter of the present disclosure relates to a method comprising coating a substrate with the alloy of a powder mixture containing Ag and Ni, Ag and Fe, Ag, Ni and Cu or Ag, Fe and Cu. Preferably, such coating processes include roll bonding, physical vapor deposition, and cold spraying.

The following Examples further detail and explain the preparation and performance of the inventive metal alloys for improved wear resistance. Those skilled in the art will recognize many variations that are within the spirit of the invention and scope of the claims.

EXAMPLES Fabrication of Alloys

Unless otherwise specified, the alloys in the examples are prepared as follows. Commercially pure powders (selected from Ag, Ni, Fe and Cu) are combined in the atomic amounts specified and then subjected to high-energy ball milling using a SPEX 8000 mill in an argon glove box for 12 h at ambient temperature (50° C.). Ball milling forces the mixing of matrix and Ag into a nanocomposite. The ball-milled powders are then compacted by warm pressing at 300° C. with a 1 GPa load under high vacuum (1.5×10⁻⁸ torr), producing cylinders with density exceeding 99% of the theoretical density. Limited contamination of powders can occur during ball milling by milling tools; e.g., when Fe is the matrix, small Fe₂O₃-type precipitates can be formed during compaction and annealing. The size and density of these nanoscale precipitates can be measured by Z-contrast imaging. Lastly, hardness is measured by nanoindentation, which is performed by ASTM E2546.

Wear Testing

Pin-on-disk wear tests are performed in air under 1 kgf load (1.38 MPa nominal pressure) using either a martensitic stainless steel 440C disk or a Cu—Ni—Sn bronze disk as the counterface material, using a procedure ASTM G99-05. A sliding velocity of 0.25 m/s is selected to suppress flash heating at the contacting surfaces, and local pin temperature measurements yield temperatures between 60 and 70° C. Continuous measurements of the pin displacement and of the frictional force establish that wear has reached a steady state when sliding distances exceed 60 m. Steady-state wear rates are calculated by weight loss measurements after sliding distances of 450 m. Prior to wear testing, the contacting surfaces of the sample and disk are mechanically polished to achieve an average surface roughness (Ra) of less than 200 nm, as measured by a Sloan Dektak ST stylus surface profilometer. Three separate tests are run for each specimen, and the average wear rates and coefficients of friction recorded.

Microstructural and Mechanical Characterization

The microstructures of the worn samples are characterized by TEM and STEM, including high-angle annular dark field (HAADF) imaging and energy-dispersive spectroscopy (EDS), using JEOL 2010 TEM and STEM microscopes operated at 200 kV. The directions normal to the sliding surface, along the sliding direction and perpendicular to the sliding direction in the sliding plane are defined as ND, SD and TD, respectively. ND-SD and ND-TD cross-sectional TEM samples are prepared.

Ni₉₀Ag₁₀, Ni₈₀Ag₂₀, Ni₈₀Cu₁₀Ag₁₀, pure Ni and Ni₄₅Cu₄₅Ag₁₀ are prepared using the methods described above. FIG. 1 shows the X-ray diffraction patterns of two samples. Since Ni is completely miscible with Cu but completely immiscible with Ag, the peaks of the Cu—Ni-rich fcc phase in the ternary alloy are shifted to smaller 2-theta angles compared to pure Ni (both Cu and Ag have a larger lattice parameter than Ni). Cu has some small but limited solubility in Ag, resulting in a shift of the peaks of the Ag-rich phase to larger 2-theta angles. It is known that Cu and Ag can be mixed by RT ball milling, but this unstable nanocomposite will begin to phase separate during compaction at ≈300° C.

Z-Contrast Imaging of Ni₉₀Ag₁₀ Alloy

HAADF-STEM imaging (z-contrast) of a Ni₉₀Ag₁₀ alloy shows that an as-annealed sample has equiaxed Ni and Ag precipitates, see FIG. 2a . In contrast, after wear, they evolved to elongated Ni and Ag rich layers. At the depth of about 5 μm, the precipitate morphology switches from an elongated layered structure to an equiaxed structure, close to the initial bulk.

Characterization of Worn Surface and Wear Debris

In order to better determine the role of Ag layering on wear rate and wear mechanisms, the morphology of the wear track and the morphology and the composition of the debris generated during sliding wear were analysed. The as-pressed and the annealed Ni₉₀Ag₁₀, Ni₈₀Ag₂₀ and Ni₈₀Cu₁₀Ag₁₀ alloys were analysed. The worn surface morphology is indicative of both severe adhesive and abrasive wear, but the dominant wear mechanism is severe adhesive wear, as seen in FIG. 3(a,d) from the elongated patches of material, smeared onto the sliding surface. Wear debris contains both fine particles and large flakes, see FIG. 3(b, e). Energy dispersive X-Ray spectroscopy (EDX) analysis shows that for binary alloys, the debris are composed of Ni, Ag and iron oxides formed between the surface materials and the environment, as shown in FIG. 3c . For the ternary alloy, as expected Cu is also found in the wear debris, as shown in FIG. 3 f.

Fabrication, Characterization, and Testing of Ni—Ag-Base Alloys

Five compositions were prepared: pure Ni, Ni₉₀Ag₁₀, Ni₈₀Ag₂₀, Ni₈₀Cu₁₀Ag₁₀, and Ni₄₅Cu₄₅Ag₁₀ using the methods described above. Samples from these alloys were also annealed to vary the initial size of the Ag precipitates. These alloys are characterized by x-ray diffraction and transmission electron microscopy. It can be seen that sliding wear can induce chemical nanolayering in Ni—Ag, see FIG. 4, and Ni—Cu—Ag alloys. More importantly, it is shown that if the initial Ag precipitate size is too large, typically ≈1 μm or more, nanolayering could not fully develop, most likely because the strain imposed by wear is then insufficient to achieve layering. This lack of nanolayering resulted in a very significant increase in wear rate, as shown in FIG. 5. Moreover, it was found that if the initial Ag precipitate size is too small, while nanolayering does take place, improvement in wear resistance is not optimal. The existence of an optimum initial Ag precipitate size for wear resistance is an important fundamental result, which has important practical consequence on the rational design of self-organized wear resistant materials

Other features, advantages and embodiments of the invention disclosed herein will be readily apparent to those exercising ordinary skill after reading the foregoing disclosure. In this regard, while specific embodiments of the invention have been described in considerable detail, variations and modifications of these embodiments can be effected without departing from the spirit and scope of the invention as described and claimed. 

We claim:
 1. A two-phase metallic alloy comprising precipitates of Ag possessing a volume-averaged diameter of less than about 500 nm dispersed in a matrix selected from the group consisting of Ni, Fe, combinations of Ni with Cu and combinations of Fe with Cu.
 2. The two-phase metallic alloy of claim 1 wherein the precipitates of Ag are immiscible in the matrix.
 3. The alloy of claim 1 wherein the matrix is Ni.
 4. The alloy of claim 3 wherein the Ag precipitates possess a volume-averaged diameter of from 100 to 400 nm.
 5. The alloy of claim 4 wherein the Ag precipitates possess a volume-averaged diameter of from 100 to 300 nm.
 6. The alloy of claim 3 wherein Ag is present in an amount ranging from about 5 to about 20 atomic percent and Ni is present in the alloy in an amount ranging from about 50 to about 95 atomic percent.
 7. The alloy of claim 3 wherein the matrix further comprises Cu.
 8. The alloy of claim 7 wherein Ag is present in an amount ranging from about 5 to about 20 atomic percent, Ni is present in an amount ranging from about 50 to about 90 atomic percent and Cu is present in an amount ranging from about 5 to about 45 atomic percent.
 9. The alloy of claim 1 wherein the matrix is Fe.
 10. The alloy of claim 9 wherein the Ag precipitates possess a volume-averaged diameter of from 100 to 400 nm.
 11. The alloy of claim 10 wherein the Ag precipitates possess a volume-averaged diameter of from 100 to 300 nm.
 12. The alloy of claim 9 wherein Ag is present in the alloy in an amount ranging from about 5 to about 20 atomic percent and Ni is present in the alloy in an amount ranging from about 5 to about
 20. 13. The alloy of claim 9 wherein the matrix further comprises Cu.
 14. The alloy of claim 13 wherein Ag is present in an amount ranging from about 5 to about 20 atomic percent, Fe is present in an amount ranging from about 50 to about 90 atomic percent and Cu is present in an amount ranging from about 5 to about 45 atomic percent.
 15. A method of making a two-phase metallic alloy, comprising providing a powder mixture selected from the group consisting of powder mixtures of Ag and Ni; Ag and Fe; Ag, Ni and Cu; and Ag, Fe and Cu; subjecting the powder mixture to high-energy ball milling to provide a nanocomposite; compressing the nanocomposite to provide a solid form; and optionally, annealing the solid form to provide a two-phase metallic alloy comprising precipitates of Ag possessing an average size of less than about 500 nm.
 16. The method of claim 15 wherein the two-phase metallic alloy comprises a wear surface and chemical nanolayering below the wear surface.
 17. The method of claim 15 wherein the powder mixture is Ag and Ni.
 18. The method of claim 17 wherein the powder mixture of Ag and Ni has an atomic formula of Ni₉₀Ag₁₀ or Ni₈₀Ag₂₀.
 19. The method of claim 15 wherein the powder mixture is Ag and Fe.
 20. The method of claim 15 wherein the powder mixture is Ag, Ni and Cu.
 21. The method of claim 15 wherein the powder mixture is Ag, Fe and Cu.
 22. The method of claim 21 wherein the powder mixture of Ag, Fe and Cu has an atomic formula of Ni₈₀Cu₁₀Ag₁₀ or Ni₄₅Cu₄₅Ag₁₀.
 23. An article comprising the alloy of claim
 1. 24. A substrate coated with the alloy of claim
 1. 25. A method comprising coating a substrate with the alloy of claim
 1. 26. A two-phase metallic alloy comprising precipitates of Ag possessing a volume-averaged diameter of less than about 500 nm dispersed in a matrix selected from at least one of W, Mo, Cr, Ni, C, Al, Ti, Cu, Fe, Mn, S, Si, N, Co, and Nb, wherein at least one of Ni or Fe is present in an amount of at least 35 atomic percent on the basis of the metallic alloy.
 27. The two-phase metallic alloy of claim 26 wherein the matrix is selected from at least one of W, Mo, Cr, Ni, C, Al, Ti, Cu, Fe, Mn, S, Si, N, Co, and Nb.
 28. The two-phase metallic alloy of claim 26 wherein the matrix is selected from at least one of W, Mo, Cr, Ni, C, Al, Ti, Fe, Mn, S, Si, N, Co, and Nb.
 29. The two-phase metallic alloy of claim 28 wherein the matrix is selected from at least one of Ni, Fe, Cr, Mo, Ti, and W.
 30. The two-phase metallic alloy of claim 29 wherein the matrix is selected from at least one of Ni and Fe.
 31. The two-phase metallic alloy of claim 26 wherein the matrix is selected from Incoloy® Alloy 330, Incoloy® Alloy 800, Incoloy® Alloy 800H, Incoloy® Alloy 800HT, Incoloy® Alloy 803, Incoloy® Alloy 840, Incoloy® Alloy 890, Inconel® Alloy 600, Inconel® Alloy 601, Inconel® Alloy 617, Nickel 200, Nickel 201, Duranickel® Alloy 301, Monel® Alloy 400, Monel® Alloy R-405, Monel® Alloy K-500, Inconel® Alloy 800, Inconel® Alloy 22, Inconel® Alloy 625, Inconel® Alloy 625SLCF®, Inconel® Alloy 686, Inconel® Alloy 690, Inconel® Alloy C-276, Inconel® Alloy G-3, Incoloy® Alloy 800, Incoloy® Alloy 825, Incoloy® Alloy 864, Incoloy® Alloy 20, or Incoloy® Alloy 25-6HN.
 32. The two-phase metallic alloy of claim 28 wherein the matrix is selected from Incoloy® Alloy 330, Incoloy® Alloy 800, Incoloy® Alloy 800H, Incoloy® Alloy 800HT, Incoloy® Alloy 803, Incoloy® Alloy 840, Incoloy® Alloy 890, Inconel® Alloy 600, Inconel® Alloy 601, Inconel® Alloy 617, Nickel 200, Nickel 201, Duranickel® Alloy 301, Inconel® Alloy 800, Inconel® Alloy 22, Inconel® Alloy 625, Inconel® Alloy 625SLCF®, Inconel® Alloy 686, Inconel® Alloy 690, Inconel® Alloy C-276, Incoloy® Alloy 800, Incoloy® Alloy
 864. 